The Cell Separation and Quantitative Transplantation Core will support investigators and projects on this Program Project Grant (PPG) by providing cell populations highly enriched for hematopoietic stem and immature precursor cells for in vitro and in vivo experiments;by providing multi-parameter flow cytometric analysis of cells from transplanted animals and in vitro cultures;and by performing competitive and quantitative transplantation studies. The Core will perform cell staining, cell separations, cell sorting and analysis using flow cytometry for investigators on the PPG. The Core will perform in vivo transplantation studies for investigators to quantify the long-term marrow repopulating function of cell populations produced by the different Projects. To facilitate analysis of marrow repopulation by donor cells the Core will use transplant recipients of the appropriate congenic strains (e.g. CD45.1 vs. CD45.2) in which donor cells can easily be distinguished from competing or residual host cells. The core will perform all the transplants, irradiating, infusing and maintaining animals after transplant as well as collecting specimens for all the investigators in the PPG. The Core will perform analysis of cells from transplanted animals to quantify donor cell engraftment in different hematopoietic lineages. The Core provides an efficient use of resources by being able to isolate uniform populations of cells for multiple projects and collaborating investigators at the same time, and by coordinating transplantation studies between projects so that common groups of control animals are used, thereby decreasing animal usage.